Results of tension compression fatigue test of low frequency gray cast iron
Among the 8 samples of low-alloy HT250 low-frequency tension compression fatigue test, 50% passed the low-frequency tension compression test, 50% failed the low-frequency tension compression fatigue test, and the failure samples were all in the working section, belonging to normal fracture.
Tension compression fatigue test results of high frequency gray cast iron
In the 16 samples of high frequency tension compression fatigue test of low alloy HT250, 50% passed the high frequency tension compression fatigue test and 50% failed the high frequency tension compression fatigue test. The fracture positions of failed samples are working sections, which belong to normal fracture.
Tensile compressive fatigue fracture morphology of gray cast iron under different loading frequencies
The tensile compressive fatigue fracture morphology of low alloy HT250 under different loading frequencies is shown in the figure.
Figure (a) and (b) show the 30x morphology of tension compression fatigue fracture of low alloy HT250 under different loading frequencies. It can be seen from the figure that there is no obvious bright source area on the surfaces of low-frequency tension compression fatigue fracture and high-frequency tension compression fatigue fracture. The surfaces of the two fractures are black and uneven, but the point like radial crack source can be seen on the surfaces of the two fractures, which is also called “river pattern”, Figure (c) (d) shows the 500X morphology of tension compression fatigue fracture of low alloy HT250 under different loading frequencies. It can be seen from the figure that there are obvious tearing edges and smooth cleavage surfaces on the surfaces of the two fracture surfaces, showing the characteristics of quasi cleavage fracture, figure (E) (F) It is the 1000x morphology of tension compression fatigue fracture of low alloy HT250 under different loading frequencies. It can be seen from the figure that there are fatigue bands on the surface of the two fracture surfaces. The fatigue bands are usually considered to be formed by the combination of some grooves or protrusions. With the emergence of cracks, they expand with the extension of cracks. The emergence of fatigue bands indicates that the grains have certain toughness, and each fatigue stripe corresponds to the loading load A cycle of charge.
Low frequency (20Hz) and high frequency (130-140hz) The passing rate of the tensile compression fatigue test on the test sample is 50%, and the tensile compression fatigue fracture of both have obvious fatigue fracture characteristics, which belongs to normal fatigue fracture. In conclusion, the loading frequency of gray cast iron fatigue test between 20hz-140hz will not have a significant impact on the fatigue performance of gray cast iron. In order to speed up the test progress, high-frequency fatigue testing machine and The load frequency is 130hz-140hz.